The use of electromagnetic (EM) energy in the heating arts has been utilized for many years. In recent years EM energy has been utilized in diathermy and hyperthermia to provide therapeutic heating to diseased tissue.
The use of heating for cancer therapy is commonly called hyperthermia which is one of the intended uses of this invention. This may be in combination therapies with other treatments such as surgery, ionizing radiation, and chemotherapy. In such treatments it is common to attempt heating the diseased tissue to above 42 degrees C., but often undesirable complications occur when the maximum tissue temperature exceeds 45 to 46 degrees C. Some of these complications include damage to healthy normal tissue, ulceration, and higher incidence of surface blisters and burns The application of the frequencies used have typically ranged from 100 KHz to 2450 MHz.
A recently popular practice has been the use of coaxial dipole radiators of very small cross-sectional size which were inserted directly into the tissue through implanted catheters. This method has enabled a great deal of flexibility for the therapist to position the heating applicators at the location of the diseased tissue only. The method has been called interstitial hyperthermia. The most common types of interstitial are the microwave interstitial (MI) and local current fields (LCF). The microwave interstitial array methods utilizing synchronous fields at the same frequency was first disclosed in U.S. Pat. No 4,448,198. This method and system used several microwave interstitial dipole antennae which were placed within interstitially placed catheters. This type of array could utilize many antennae, but were constrained to be placed along a circular circumference so as to surround a target zone The synchronous operation of each applicator with the same or fixed relative phase would provide substantially improved heating in the tissues within the central zone of the array. This method did not include arrays of these antennae placed along a straight or partially curved line This method did disclose the use of phase shifters to modify the phase of each antenna. One method to accomplish this phase shift was the use of motorized positioning systems under computer control to move and position the antenna coaxial cable.
U.S. Pat. No. 4,669,475 issued June 2, 1987 discloses the same system modified with improved antennae designs to provide tip heating and contain integral thermometry sensors within the antenna heating tip area. This patent also disclosed the use of independent phase and amplitude steering to control the heating zone. This method and equipment was also exclusively described as an internal or interstitial use of these small dipole antenna.
Another system is known using centrally placed dipole antennae in the central zone of such arrays. These central antennae accomplish a partially destructive interference of the central energy focus which is often too hot. This method also utilizes microwave interstitial arrays which are placed into catheters which are in dwelling within the tissues to be heated (U.S Patent Application Serial No. 161,456, BSDM B5578).
Other U.S. patent prior art which have been cited relevant in similar applications are Hansjurgens U.S Pat. No. 3,774,620, Leveen U.S. Pat. No. 4,095,602 Wyss et al., U.S. Pat. No. 4,148,321, Armitage U.S. Pat. No. 4,285,346, Gammell U.S. Pat. No. 4,346,715, Sterzer U.S. Pat. No. 4,190,053, Paglione U.S. Pat. No. 4,204,549, Sterzer U.S. Pat. No. 4,311,154, Brisson U.S. Pat. No. 4,322,594, Vaguine U.S. Pat. No. 4,397,313, and U.S. Pat. No. 4,397,314, Cosman U.S. Pat. No. 4,411,874, and Whalley U.S. Pat. No. 4,237,898.
Another method and device uses capacitive coupling to transfer lower frequencies such as 1 to 100 MHz through an in-dwelling catheter into the tissue to be heated. This design relies upon capacitive applicators acting as electrodes. That is, they operate in pairs having opposite voltage polarities, or they work with a larger metal plate or structure to act as the opposite polarity electrode. In this way high frequency currents are made to flow between these opposing polarity structures and though the intervening tissue, thereby heating the tissue. These antennae were described as being completely within tissue to be heated (U.S. Pat. No. 4,712,559 issued Dec. 15, 1987).
The use of electromagnetic heating has also been applied externally to the tissue surface through either tissue contacting or noncontacting applicators. These have most commonly been in the form of metallic capacitive plates or microwave antenna (usually in the form of waveguides). The problem with these two external methods is that except for the intensity of the heating field, the heating distribution is not controllable Thus, these common techniques often result in poor heating of substantial portions of diseased tissue or in excessive heating of tissues.
In an effort to more fully provide flexibility for deep heating target tissue zones, a device was developed and described in U.S. Pat. No. 4,462,412 issued July 31, 1984. This system includes an annular phased array device which was a rigid array of 16 external applicators of the waveguide form which surrounded the body in a cylindrical or annular manner. This also included the use of a high dielectric fluid such as water to fill the area between the applicators and the tissue surface. Such annular phased array device is capable of providing selective and deep hyperthermia and utilizes the phase and power amplitude steering of EM energy. The selection of frequency was related to the diameter of the tissue cross-section which was to be deeply heated. This device did not claim any particular advantages in the heating or treatment of surface or superficial disease sites. The selection of the frequencies to achieve deep heating force the frequencies to be quite low which resulted in very large wavelengths These wavelengths were typically 30 cm long within the high water tissues of the body. The control of energy could not easily be confined to zones smaller than 1/3 to 1/2 of the wavelength within the tissue. Thus, the problem with this system is that it provides fairly poor heating control for superficial treatments where the heating pattern would need to be adapted to locally different heating and cooling effects.
A similar but more advanced cylindrical annular phased array device is disclosed in U.S. Pat. No. 4,589,423, issued May 20, 1986. This device is similar to the first annular array patent, but uses external dipoles in a phased array approach This design is intended to provide deep and central tissue heating by surrounding the target tissue zone with energy from all surface sides to maximize the delivery of energy at a particular deep zone. This design utilizes several external dipole antennae along the perimeter of a high dielectric annular envelope called a bolus which separated the dipoles from the tissue surface. A problem with known devices using boluses is that they prevent viewing the tissue surface during heating and the positioning of the applicators and temperature sensors. In this device again the frequencies used to achieve deep heating are so low that control of heating selectively along the surface and subsurface tissues is a problem. The typical frequency described for a 20 to 30 cm diameter tissue regions was 100 MHz. This frequency provided a 27 cm wavelength within the high water tissues. Selective alteration of the heating field was not very precise along the surface zones. This design was also described in detail in a published article by Turner entitled "Mini-Annular Phased Array for Limb Hyperthermia", IEEE Trans. on MTT, Vol. MTT-34, No. 5, pp. 508-513, May 1986.
Another approach was published by Sterzer et al. entitled "RF Therapy for Malignancy", IEEE Spectrum, December 1980, pp. 32-37. This article described a very high frequency array of micro-strip dipole antennae mounted on a ridged dielectric substrate where a dielectric powder (bean-bag) was placed between the antennae and the tissue surface. The described operating frequency was 2450 MHz. This device did not contain any provisions for altering the power amplitude or phase of the radiating antennae. Thus, little practical clinical use has been made of this design because of its inflexibility to adapt its heating to the requirements of the tissue being heated.
A further problem with known hyperthermia devices using applicators containing tubes is that electromechanical positioning means have not been included for selectively positioning the applicators in the tubes for and during treatment.